The present invention relates to implantable hemodynamic monitors (IHMs). Specifically, the invention relates to a device that interfaces with various hospital monitoring systems and various equipments fabricated by different manufacturers to transfer data from the IHMs to hospital monitoring systems. More specifically, the invention pertains to a data management interface system that is compatible with various models of monitoring equipment built by different manufacturers. Further, the invention relates to a data management system that connects IHMs and a remote monitoring system to transfer the patient""s medical data and information to an expert data station center where expert systems and personnel are stationed to monitor patients located in various hospital rooms and/or wards.
Health care professionals are fully aware of the need to monitor, on a frequent or continuous basis, the vital signs associated with hospitalized patients, particularly those who are seriously and chronically ill. Virtually every hospitalized patient requires periodic measurement and logging of blood pressure, temperature, pulse rate, etc. This type of monitoring has typically been performed by having a health care worker periodically visit the bedside of the patient and measuring and/or observing the patient""s vital signs using dedicated equipment that is either hooked up to the patient or brought into the patient""s room. Current monitoring procedures are not ideally cost effective because of being highly labor intensive. Moreover, if an invasive procedure is used, the need to continuously monitor the patient becomes critical because of the associated risk.
To alleviate such concerns, hospitals have adopted new and improved patient monitoring methods and processes. The two most frequently used are 1) intensive care wards and 2) xe2x80x9cstepped downxe2x80x9d care or xe2x80x9cmonitored bedxe2x80x9d wards. In an intensive care ward, physicians and staff check the patient frequently and directly observe pressure signals on the bedside monitor. This bedside monitor is usually connected, via hardwire, analog or digital, to a central nurses""station where the pressure can be continuously watched or observed. These readings can also be documented by placing them in digital storage such as a disk, for example, or printed on paper for inclusion in the patient""s file. A xe2x80x9cstepped downxe2x80x9d ward is a less intensive setting in which the patient can be monitored as described above. In either case, the pressure monitors may be hardwired or connected via RF to central monitoring stations.
A great many implantable medical devices (IMDs) are currently used for cardiac monitoring and/or therapy. Generally, these devices include sensors located in a blood vessel or heart chamber and coupled to an implantable monitor or therapy delivery device. For example, IMDs include implantable heart monitors, therapy delivery devices such as pacemakers, cardioverter/defibrillators, cardiomyostimulators, ischemia treatment devices, and drug delivery devices. Typically, these cardiac systems include electrodes for sensing and sense amplifiers for recording and/or deriving sensed event signals from the intracardiac electrogram (EGM). In current cardiac IMDs that provide a therapy, the sensed event signals are used to control the delivery of the therapy in accordance with an operating algorithm. Selected EGM signal segments and sensed event histogram data or the like are stored in internal RAM for data telemetry via an external programmer at a later time.
Efforts have also been underway for many years to develop implantable physiologic signal transducers and sensors for temporary or chronic use in a body organ or vessel usable with such IHMs for monitoring a physiologic condition other than, or in addition to the disease state that is to be controlled by a therapy delivered by the IMD. A comprehensive listing of implantable therapy delivery devices are disclosed in conjunction with implantable sensors for sensing a wide variety of cardiac physiologic signals in U.S. Pat. No. 5,330,505, incorporated herein in its entirety by reference.
Typically, an IHM measures right ventricular (RV) blood pressure that stems from changes in cardiac output that may be caused by a cardiac failure, ventricular tachycardia, flutter, or fibrillation. These variations may reflect a change in the body""s need for oxygenated blood. An IHM may also measure temperature, a compensatory variable. Measuring temperature is used in these situations to correct for potential erroneous judgment stemming from changes in RV pressure resulting from body temperature changes. Temperature measurements have been used informally to identify disease processes not attributable to heart failure, such as the flu, which might be confused with changes in pressure that otherwise might be attributable to heart failure.
For example, as disclosed in U.S. Pat. No. 6,024,704 issued to Meador et al, monitoring of a substantial drop in blood pressure in a heart chamber, particularly the right ventricle, alone or in conjunction with an accelerated or chaotic EGM, is considered as an indicator of fibrillation or tachycardia sufficient to trigger automatic delivery of defibrillation or cardioversion shock. More recently, it has been proposed to monitor the changes in the blood pressure type (dP/dt) by comparing the absolute blood pressure rise and fall rates (dP/dt) that accompany the normal heart contraction and relaxation to those that occur during high rate tachycardia, flutter, or fibrillation.
A number of cardiac pacing systems and algorithms for processing the monitored mean blood pressure or monitored dP/dt have been proposed and, in some instances employed clinically, for treating bradycardia. Such systems and algorithms are designed to sense and respond to changes in mean blood pressure or dP/dt, to change the cardiac pacing rate (rate responsive pacing) between an upper and a lower pacing rate limit in order to control cardiac output.
Such IHMs, blood pressure, and temperature sensors that derive absolute blood pressure signals and temperature signals are disclosed in commonly assigned U.S. Pat. Nos. 5,368,040, 5,535,752 and 5,564,434, and in U.S. Pat. No. 4,791,931 all incorporated by reference herein. The MEDTRONIC(copyright) Chronicle(copyright) Implantable Hemodynamic Monitor (IHM), disclosed in U.S. Pat. Nos. 6,024,704 and 6,152,885 both incorporated herein by reference in their totality, employs the leads and circuitry disclosed in the above-incorporated, commonly assigned, ""752 and ""434 patents to record absolute blood pressure values for certain intervals. The recorded data is transmitted to a programmer preferably under the control of a physician in an uplink telemetry transmission from the IHM. As is well known in the art, a telemetry session is initiated by a downlink telemetry transmission from the programmer""s radio frequency (RF) head and receipt of an interrogation command by the IHM.
Thus, in accordance with the disclosures in the ""704 and ""885 patents, an IHM for deriving an absolute pressure signal value is coupled and compared with a barometric reference signal using implantable physiologic sensor(s) to determine a resultant nonabsolute cardiac pressure signal values for storage and transmission. Further, the patents (""704 and ""885) disclose a system of calibration of the reference pressure and/or temperature sensor in relation to an external, calibrated, barometric pressure and/or body temperature sensor. This system may be implemented to interlace digital signal values (related to pulmonary artery diastolic pressures) with the primary cardiac pressure signal values derived from the right ventricle, as disclosed in U.S. Pat. No. 6,155,267 incorporated herein by reference.
In accordance with the present invention, an IHM may be implanted in a rather broadly defined group of patients. The requirements for implant include symptomatic heart failure of at least 3 months duration. These are the sickest patients who consume a large percentage of health care dollars. They require frequent hospitalization and frequent catheterizationsxe2x80x94both of which require large expenditures in resources and money, and pose great risk to the patient. When implanted, the IHM is used to monitor the progression of a patient""s disease and tune up medications as needed. The medical objective for these patients is to manage them non-invasively within a less intensive clinical setting or as outpatients in a home setting. With trans-telephonic monitoring from their home, they would perhaps require even fewer clinic visits.
Generally, these patients frequently require hospital visits, even if placed in out-of-hospital settings. Nearly 70% of patients may need hospitalization in the first year of medical care for heart failure. Higher percentages of hospitalizations may be encountered post-implant. The present invention provides significant cost reductions while enhancing the quality of care of heart failure patients, both in the hospital and at home.
Heart failure is a progressive disease and, while treatment slows the progression, the disease is not currently curable. Once the patients are hospitalized, there is still no known method or device, to continuously monitor them, except to use a dedicated IHM programmer that must be implanted to gain access to the pressure waveform. Only trained clinicians can currently uplink the data and this is available only when such medical personnel are present. The dedicated programmer (one per bed) is also expensive. In addition, the programming head must be held over the IHM, thus making it impracticable for continuous monitoring of the patients. The present invention enables uninterrupted continuous monitoring by nursing staff or healthcare providers via standard equipment which is commonly available in hospitals and care centers.
The present invention provides an interface that enables the transfer of a hospital patient""s medical data to any of the existing monitoring systems fabricated by over forty different manufacturers. These monitoring systems, in turn, are connected via telemetry to a remote data center, to display medical data in real time to expert personnel (e.g., trained nurses, technicians, etc.) within a hospital. Although the IHM system used to collect data that is passed through the interface described herein is currently limited to the measurement of cardiac pressure, IHM devices may be adapted to detect and transmit other physiologic signals (such as Oxygen saturation, pulmonary artery diastolic pressure, systolic pressure, temperature, etc,) via the interface described herein.
Transferring real-time signals from the IHM into various bedside monitors that are manufactured by various manufacturers, would normally be difficult because of compatibility across the various monitors. Transmitting signals from the IHM on a universal basis would normally require a significant investment in acquiring the external bedside monitor from each manufacturer and communications protocols to comply with various standards. The task is made somewhat easier because the IHM typically measures cardiac pressure at this time. There are many available commercial bedside monitors that use industry-standard extra-corporeal pressure transducers. For example, there are over one hundred different models from over forty separate manufacturers that are compatible with the Abbot Critical Care""s Transpac IV transducer.
With this in mind, the present invention applies calibrated, real-time pressure signals from the IHM to a circuit that mimics the Abbott Transpac IV circuit (see FIG. 4). The resultant pressure signal to the bedside monitor is compatible with the input characteristics of this commercial device.
The present invention makes use of an IHM system that determines the hemodynamic status of a patient from measurements of estimated pulmonary arterial diastolic pressure and right ventricular pressure obtained from a single absolute pressure sensor implanted in the right ventricle. Both of these measurements have been shown to correlate with the degree of cardiac failure of a patient. The IHM system continually monitors the right ventricular pressure using an absolute pressure sensor and marks the right ventricular pressure at the moment of specific events.
The IHM system may be used in clinical indications that require the measurement of hemodynamic status and, includes but is not limited to, in the diagnosis of the severity of congestive heart failure, pulmonary artery disease, and pulmonary hypertension or the measurement of hemodynamic variables like vascular resistance, contractility, etc. For example, the maximum dP/dt signal derivation capability of the IHM system can also approximate contractility; and the RV diastolic pressure in combination with mean arterial pressure (e.g. measured by a cuff) and a separate measure of cardiac output (measured either invasively or noninvasively) to provide a measure of vascular resistance.
The present invention provides an apparatus and method to enable physicians to view pressure curves available via real-time telemetry, other than by using the programmer. Under current practice, the physician uses a programmer to view the real-time pressure wave along with the EGM tracing. Using the present invention, the IHM system will be able to telemeter real-time signals to any one of a large number of standard monitoring devices. Modules already exist in these sensing devices for monitoring pressure. These modules are routinely used coupled to another signal source, such as a pressure transducer. The present invention is implemented to provide a bridge between the RF telemetered, real-time signal produced by the IHM system and convert that signal to one that approximates the signal these monitoring devices receive from a standard pressure transducer.
Generally, patients will have a standard monitoring system at a bedside for noninvasive monitoring. The IHM system provides a pressure signal comparable to a commercially available catheter. Detecting the signal from the implanted IHM system may be accomplished via several means such as, for example, a lightweight rubber antenna. This antenna may be attached to the patient""s clothing or draped over the patient""s shoulder, and is then connected to a small telemetry/signal-conditioning box dedicated to this function. The box is then connected to the interface disclosed in the present invention and then to the bedside monitoring device via a standard cable.
Extra-corporeal pressure transducers have been standardized so that many bedside monitors work with several manufacturers"" pressure transducers. The circuitry driving the transducers has also been standardized. Accordingly, an interface can be fabricated that mimics the pressure transducer""s signals. The interface should also function in cooperation with many standard monitoring systems/devices. The present invention enables these and many other features to enable reliable and continuous remote monitoring of patients while minimizing health care costs.